A science teacher claims that it is possible to lose weight even after eating junk food on a regular basis.

A 2004 American documentary "Super Size Me" showed Morgan Spurlock, an American independent filmmaker, who ate only McDonald's food three times a day for a continuous 30-day period.

As a result of a complete McDonald's diet, the then-32-year-old Spurlock claimed to gain 24.5 pounds, a 13 percent increase in body mass and a cholesterol level of 230. Spurlock also experienced mood swings, sexual dysfunction and fat accumulation in his liver. It took Spurlock fourteen months to lose the weight gained using a vegan diet supervised by his future wife.

However, John Cisna, a science teacher in the Colo-Nesco School District, went on a McDonald's only diet for 90 days and interestingly lost weight.

"I can eat any food at McDonald's (that) I want as long as I'm smart for the rest of the day with what I balance it out with," Cisna told local TV station KCCI.

The science teacher approached the owner of a local McDonald's franchise who agreed to provide 90 days of meals to Cisna free of cost.

Cisna ate McDonald's food three times a day: breakfast, lunch and dinner. However, Cisna followed strict daily nutritional limitations of 2,000 calories. The science teacher tried to follow the recommended daily dietary allowances for nutrients such as carbohydrates, proteins, fat calories and cholesterol.

Cisna took the help of three of his students who used McDonald's online nutritional information to build daily meals for their teacher to ensure that he is on track with the nutritional limitations.

"So this isn't something where you say 'well he went to McDonalds and he only had the salads. No, I had the Big Macs, the quarter pounders with cheese.  I had sundaes, I had ice cream cones," added Cisna.

During the course of the 30-day experiment period, Cisna started walking for 45 minutes a day. Cisna reports that by the end of the ninetieth day he lost 37 pounds and his cholesterol dropped from 249 to 170.

Cisna says that the reason for the experiment is not to encourage people to eat more at McDonald's but to pay attention to the daily nutritional requirement of the body.

"The point behind this documentary is, 'Hey, it's (a) choice. We all have choices. It's our choices that make us fat not McDonald's," added Cisna.